1. Field of the Invention
The invention relates to toner processes, and more specifically to aggregation and coalescence processes for the preparation of toner compositions. More in particular, the invention relates to a method of preparing a toner composition by the emulsion aggregation technique in which the ionic coagulant is added into the composition in stages instead of all at the same time during homogenization.
2. Discussion of Related Art
In forming toner compositions for use with reprographic or xerographic print devices, emulsion aggregation processes are known. For example, emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. No. 5,290,654, U.S. Pat. No. 5,278,020, U.S. Pat. No. 5,308,734, U.S. Pat. No. 5,370,963, U.S. Pat. No. 5,344,738, U.S. Pat. No. 5,403,693, U.S. Pat. No. 5,418,108, U.S. Pat. No. 5,364,729, and U.S. Pat. No. 5,346,797. Also of interest may be U.S. Pat. Nos. 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935 (spherical toners).
In addition, the following U.S. patents relate to emulsion aggregation processes of forming toner compositions, the disclosures of which are incorporated herein by reference in their entireties:
U.S. Pat. No. 5,922,501 describes a process for the preparation of toner comprising blending an aqueous colorant dispersion and a latex resin emulsion, and which latex resin is generated from a dimeric acrylic acid, an oligomer acrylic acid, or mixtures thereof and a monomer; heating the resulting mixture at a temperature about equal, or below about the glass transition temperature (Tg) of the latex resin to form aggregates; heating the resulting aggregates at a temperature about equal to, or above about the Tg of the latex resin to effect coalescence and fusing of the aggregates; and optionally isolating the toner product, washing, and drying.
U.S. Pat. No. 5,945,245 describes a surfactant free process for the preparation of toner comprising heating a mixture of an emulsion latex, a colorant, and an organic complexing agent.
U.S. Pat. No. 5,391,456 describes a process for the preparation of toner compositions comprising: (i) forming a dispersion of resin in an aqueous ionic surfactant solution; (ii) preparing pigment dispersions in water of three different pigments each of a dissimilar color, each dispersion being comprised of a pigment dispersed in water and which preparation utilizes nonionic dispersants, and optionally an ionic surfactant; (iii) blending the prepared resin dispersed as a latex with two, or optionally three of the different color pigment dispersions of step (ii); (iv) adding an aqueous solution of counterionic surfactant as a coagulant to the formed resin-pigment blends, while continuously subjecting the mixture to high shear, to induce a homogeneous gel of the flocculated resin-pigments blend; (v) heating the above sheared gel at temperatures between about 20.degree. C. and about 5.degree. C. below the glass transition temperature (Tg) of the resin while continuously stirring at speeds between about 200 and about 500 revolutions per minute to form statically bound toner sized aggregates between about 2 and about 12 microns in average volume diameter with a narrow size dispersity and with a geometric size distribution (GSD) between 1.10 and 1.25; (vi) heating the statically bound aggregated particles at temperatures of from between 25.degree. C. and 40.degree. C. above the Tg of the resin to form coalesced rigid particles of a toner composition comprised of polymeric resin, and pigment agent; and optionally (vii) separating and drying said toner.
U.S. Pat. No. 5,482,812 describes a process for the preparation of toner compositions or toner particles comprising: (i) providing an aqueous pigment dispersion comprised of a pigment, an ionic surfactant, and optionally a charge control agent; (ii) providing a wax dispersion comprised of wax, a dispersant comprised of nonionic surfactant, ionic surfactant or mixtures thereof; (iii) shearing a mixture of the wax dispersion and the pigment dispersion with a latex or emulsion blend comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant and a nonionic surfactant; (iv) heating the above sheared blend below about the glass transition temperature (Tg) of the resin to form electrostatically bound toner size aggregates with a narrow particle size distribution; (v) adding additional ionic surfactant to the aggregated suspension of (iv) to ensure that no, or minimal additional particle growth of the electrostatically bound toner size aggregates occurs on further increasing the temperature to coalesce the aggregates into toner particles (vi); (vi) heating the mixture of (v) with bound aggregates above about or at the Tg of the resin; and optionally (vii) separating the toner particles from the aqueous slurry by filtration and thereafter optionally washing.
U.S. Pat. No. 5,403,693 describes a process for the preparation of toner compositions with controlled particle size comprising: (i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an ionic surfactant in amounts of from about 0.5 to about 10 percent by weight of water, and an optional charge control agent; (ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant, and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin, and charge control agent; (iii) stirring the resulting sheared viscous mixture of (ii) at from about 300 to about 1,000 revolutions per minute to form electrostatically bound substantially stable toner size aggregates with a narrow particle size distribution; (iv) reducing the stirring speed in (iii) to from about 100 to about 600 revolutions per minute, and subsequently adding further anionic or nonionic surfactant in the range of from about 0.1 to about 10 percent by weight of water to control, prevent, or minimize further growth or enlargement of the particles in the coalescence step (iii); and (v) heating and coalescing from about 5 to about 50.degree. C. above about the resin glass transition temperature, Tg, which resin Tg is from between about 45.degree. C. to about 90.degree. C. and preferably from between about 50.degree. C. and about 80.degree. C. the statically bound aggregated particles to form said toner composition comprised of resin, pigment and optional charge control agent.
U.S. Pat. No. 5,977,210 describes a process for the preparation of ink compositions comprising the emulsion polymerization of monomer, water, surfactant, and initiator with stirring and heating to provide a latex; mixing therewith a pigment dispersion of pigment particles, water, and cationic surfactant; blending the mixture;
thereafter stirring the mixture; and subsequently adding additional anionic surfactant to stabilize the aggregate particles.
U.S. Pat. No. 5,622,806 describes a process for the preparation of toner compositions with controlled particle size comprising: (i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an ionic surfactant in amounts of from about 0.5 to about 10 percent by weight to water, and an optional charge control agent; (ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant, and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin, and charge control agent; (iii) stirring the resulting sheared viscous mixture of (ii) at from about 300 to about 1,000 revolutions per minute to form electrostatically bound substantially stable toiler size aggregates with a narrow particle size distribution; (iv) reducing the stirring speed in (iii) to from about 100 to about 600 revolutions per minute, and subsequently adding further anionic or nonionic surfactant in the range of from about 0.1 to about 10 percent by weight of water to control, prevent, or minimize further growth or enlargement of the particles in the coalescence step (v); (v) heating and coalescing from about 5.degree. C. to about 50.degree. C. above about the resin glass transition temperature, Tg, which resin Tg is from between about 45.degree. C. to about 90.degree. C., the statically bound aggregated particles to form said toner composition comprised of resin, pigment and optional charge control agent; (vi) washing the aggregated particles at a temperature of from about 15.degree. C. to about 5.degree. C. below the glass transition temperature of the resin, and subsequently filtering the aggregated particles until substantially all of the surfactant has been removed from the aggregated particles, followed by subsequent driving of the particles at a temperature of from about 15.degree. C. to about 5.degree. C. below the glass transition temperature of the resin; and (vii) subsequently adding to said toner product a first layer of a hydrophilic oxide, and a second layer of a hydrophobic oxide.
U.S. Pat. No. 5,863,698 describes a process for the preparation of toner comprising mixing a colorant containing a surfactant and a latex emulsion, and wherein the latex emulsion contains resin and a nonionic hydrolyzable surfactant; heating below about the resin latex glass transition temperature, followed by the addition of an anionic stabilizer, thereafter heating above about the resin glass transition temperature, and adjusting the pH of the resulting mixture of resin and colorant particles suspended in an aqueous phase containing anionic surfactant, cationic surfactant and nonionic hydrolyzable surfactant, wherein said pH is increased from about 1.7 to about 2.5 to about 6 to about 12 by adding a base during the heating above about said resin glass transition temperature wherein coalescence is being accomplished.
Finally, U.S. application Ser. No. 09/173,405 (D/98588), filed Oct. 15, 1998, incorporated herein by reference, describes a process for forming a toner by mixing a colorant, a latex emulsion and two coagulants, followed by aggregation and coalescence. The two coagulants preferably are polyaluminum hydroxy chloride and benzalkonium chloride.
None of the foregoing references describing emulsion aggregation processes for forming toner compositions describe adding the necessary counterionic coagulant in sequenced stages, and instead teach only that the coagulant is mixed into the composition at the same time prior to homogenization and aggregation. However, when adding all of the coagulant at the same time, it is difficult and time consuming to control the viscosity of the composition, and thus difficult to insure suitable homogenization and aggregation. In fact, if the composition becomes too high in viscosity, aggregation cannot be effected at all, and the composition must be disposed of.